1. Field of the Invention
The present invention relates to a semiconductor circuit device including an integrated circuit portion having an operating-frequency switching function.
2. Description of the Related Art
Semiconductor circuit devices such as a timer, a noise canceller, an SIO, and a UART have a function for switching operation processing frequencies (resolutions). A semiconductor circuit device having the function for switching operation processing frequencies is described below by referring to FIG. 13.
A signal obtained by noise-canceling a signal DVCK frequency-divided by a frequency divider 131 or an event signal EXCK input from the outside of a semiconductor chip by a digital noise canceller 132 is selected by a multiplexer 133 and used as a source clock MCK of an integrated circuit portion 135 whose operating frequency must be switched.
For example, FIG. 14 shows an operation timing chart when selecting ¼ of the source clock SCK as the operating frequency of the integrated circuit portion 135, A signal frequency-divided to ¼ of the source clock SCK by the multiplexer 133 is selected as the source clock MCK of the integrated circuit portion 135. The integrated circuit portion 135 operates (ACT) every cycle of the source clock MCK.
The prior art has a problem that it is necessary to use sync-adjusting portions such as a block 134 for sync-adjusting the interface between a block which synchronizes with the source clock SCK of the frequency divider 131 or multiplexer 133 and the integrated circuit portion 135 which is synchronizes with the source clock MCK and a block 136 for synch-adjusting the interface between a block which synchronizes with a clock ACK asynchronous with the source clock SCK and the integrated circuit portion 135.
That is, it is a problem that the response time to the signal SCK or ACK is controlled by the frequency of the signal MCK. Moreover, it is one of problems that there is a use restriction that the operating frequency (source clock of the MCK of the integrated circuit portion 135) cannot be switched during the processing operation of the integrated circuit portion 135 because whiskers may appear on the signal MCK.
As described above, there is a problem that a synch-adjusting portion is necessary because of performing sync-adjustment between a clock signal input to the frequency divider and a clock signal input to the integrated circuit portion.